Conversion of Tryptophan to Indoleacetamide and Further Conversion to Indoleacetic Acid by Plant Preparations

Sinice Kogl. Haagen-Sniit aid(I Erxlel)en (10) first reported oni the growth stimulatory properties of IAA., manv sttldies hlave l)een devoted to tracinig its rotute of biosynithesis. In 1940. Skoog alnd Thimanni (20) recognlize(d that tryp)tophan in structtural protein col(Il be converted to IAA in the preselice of proteolytic enzym-es. Sinice theln a zinumber of investigationis (6. 13. 24) has given support to the coniclusionl that tryl)tol)han is the miajor primiiary precursor of auxin. A hiost of other inldole comiipounds have been implicated as initermiiediates in the coniversioni of tryl)toplhan to IAA. Considerable evi(leilce that indoleacetaldehv-de miay lbe ani initermiiedliate has accumuiltilated (1. 5. 11). Ind(loleacetoniitrile (IAN) (7), indolepvruvic aci(l. trvptoplhol (11) anld ethvlivndoleacetate (18) are amiionig the inidole derivatives that have l)eenl reported as precursors of IAA.N. The hd(lrolvsis of 1A'N to IAA in plant tissutes (22) has led to a search for ind(loleacetamiiide (IAmu) as all initermiiediate. \Wightman (23) foullnd I.-knm to have somiie atuxini activity all(l to be hvdrolvsed in v'ivo to IAA by tomato an(l lpea. He has colnclude(d that JAmii (loes lnot occtlr as a free ilntermiiedtiate in the conversion of trvptoplhan via IAN to aulxill. O(thers (2, 3. 4. 21 ) have givenl passing nlotice to IAm as a possible biological initermiie(liate. Oln several occasions, IA.Xmi was fotull(n to be an artifact dute apl)arenltly to the prol)ensity of esters of LAA to formii an,tides in the presence of amimiomia. I'liths. Zenik (25) reported that 57 % of 1-(indole-3-acetyl) 8-dglutcose was converted to JAm (Itlrinlg paper chromiatography. Recently it has been fouiid(l that p)eroxidase catilyzes the oxidative (lecarboxylation of methiolline with the formiiationl of 3-miiethvlthiopropioinamiii(le as the product (16. 17). Several other aminio acids also un(lergo a simiiilar reactioni. \V'e have recently reporte(d the leroxi(lase-catalvzed (lecarboxylation of trvptophan to 1lAm (19). T'his has subsequently beeni conifirmiied (9). The work rel)orted in this paper gives further (letails of this reactionl anid some ol)servationls oni the further metabolism of lAm.